Generally, people all over the world drive their automobiles to various destinations. In order for these people to enjoy the ride to their destinations the suspensions systems in the automobiles must be stable and as comfortable as possible. Typically, different types of automobiles have various suspension systems, which control the ride and handling performance of the vehicle. For example, some vehicles may have a stiff suspension system that improves its handling performance, but it may provide them with an uncomfortable ride. In contrast to the stiff suspension system, some vehicles may have a soft suspension system that provides a comfortable ride, but the handling performance of this suspension system may be unbearable.
These suspension systems also include various components, such as shock absorbers. Shock absorbers receive and take up shock that would normally be exerted on the wheels of the vehicle in order to improve the ride performance and the vibration of the wheels. The vibration of the wheels triggers the suspension system to vibrate in an uncontrollable manner. The suspension system vibrates at different frequencies, which may make the suspension system unstable and arduous to control. The previously described control strategies for the suspension systems provide performance trade-off control among different mode frequencies. However, one control strategy cannot be applied to all shock absorbers to control the vibration of the different suspension systems at different frequencies.
For example, a quarter portion 101 of a known vehicle is schematically shown in FIG. 1. FIG. 1 illustrates a block diagram of the suspension system associated with a quarter portion of the vehicle body 100. Note that discussion that follows is equally applicable to the suspension systems associated with the other three portions of the vehicle. This portion 101 includes the following components: an unsprung mass 103, sprung mass 105, a spring 107 and the damper 409 (FIG. 4). These components may be connected to each other in any suitable combination. Unsprung mass 103 represents wheel 425, brake assemblies (not shown) in vehicle 400, a rear axle assembly (not shown) and other structural members not supported by the vehicle 400 (FIG. 4). Sprung mass 105 includes all the components of vehicle 400 that are supported by the suspension system of the vehicle 400.
Turning to the operation of this portion 101 of FIG. 2, as the wheel 425 traverses over a surface 111 this wheel 425 tends to vibrate. This vibration of the wheel 425 is transmitted through the suspension system of the vehicle 400 to the sprung mass 105 and unsprung mass 103. FIGS. 2 and 3 graphically illustrate the effects of a driver applying different control strategies to the suspension system of a quarter portion 101 (FIG. 1) of a vehicle. The control strategies include a light damping procedure, a hard damping procedure and a medium damping procedure. Light damping, hard damping and medium damping refers to the level of ride performance experienced by a driver in a vehicle. For example, hard damping in FIGS. 2 and 3 refer to applying a strong force to the wheels of the vehicle to stabilize them. Specifically, these figures depict the effects of light damping, medium damping and hard damping on the sprung mass components (dynamics) at a sprung mass mode of around 1.2 Hz and unsprung mass dynamics at an unpsrung mass mode of around 12 Hz, while the magnitude is indicative of the transmissibility gain or ratio. For example, in FIG. 2, when a driver applies a hard damping procedure to the vehicle 400, then the sprung mass components in the vehicle 400 have a well-controlled ride performance around the sprung-mass frequency range. In contrast to the stability of a driver applying the hard damping procedure to the vehicle 400, when the driver applies a light or medium damping procedure to the vehicle 400 the sprung mass dynamics become unstable and they can experience large vibrations near the sprung-mass mode frequency.
In FIG. 3 a driver employs a medium damping procedure to the quarter portion 101 of vehicle 100 to keep the unsprung mass components' of the vehicle 100 from fluctuating and this procedure keeps the unsprung mass dynamics well controlled. When the driver applies a light or hard damping procedure to the unsprung mass dynamics, then there will be instability in these dynamics of the vehicle. In addition, the unsprung mass dynamics may experience large vibrations. Unsprung mass dynamics and sprung mass dynamics exhibit different dynamic characteristics under different optimum damping levels corresponding to different frequencies to minimize the vibration of the unsprung mass dynamics and sprung mass dynamics, which stabilize and achieve a good ride performance of the vehicle. These figures show that one control strategy cannot be applied to all suspensions systems to control their vibration at different frequencies.
Accordingly, there is a need for a method and apparatus that enables a driver to improve the ride performance of the vehicle by stabilizing the vibration of the suspension system at any frequency.